Pattern of Instability in a Wandering Gravel Bed Channel

  1. J. D. Collinson and
  2. J. Lewin
  1. Michael Church

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch13

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Church, M. (1983) Pattern of Instability in a Wandering Gravel Bed Channel, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch13

Author Information

  1. Department of Geography, The University of British Columbia, Vancouver, British Columbia V6T 1W5, Canada

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • pattern of instability in wandering gravel bed channel;
  • channel pattern and relation to sediment movement;
  • wandering gravel bed channel;
  • pattern of instability;
  • causes of change

Summary

Bella Coola River drains 5450 km2 (7% glacierized) of the Coast Mountains and Fraser Plateau of British Columbia, whence early summer nival floods and autumn rainstorms may yield flows greater than 1000 m3 sec−1. The river flows over early post-glacial alluvial cobble gravels. Sediment entrained from the river banks and delivered from tributaries is stored in the channel principally in ‘sedimentation zones’ where the river is laterally unstable. These are connected by stable, cobble-paved ‘transport reaches’. Overall morphology is that of a ‘wandering gravel river’.

A sequence of maps beginning in the late nineteenth century shows that the river has become more stable and that the locus of lateral instability in the lower course has progressed downstream from near 25 km ca. 1900 to near the mouth today. One of two mechanisms might be invoked to explain the effect:

(i) introduction of unusual volumes of sediment into the main channel by the erosion of Neoglacial (eighteenth- and nineteenth-century) moraines of alpine glaciers, now becoming exhausted;

(ii) recent progradation of the alluvial fan at Nusatsum River constricting the main channel and blocking sediment transfer downstream.

The pattern is disturbed by sediment yield to the main channel from occasional extreme floods in tributaries.